What is Log4j? A cybersecurity expert explains the latest internet vulnerability, how bad it is and what’s at stake Posted bySantiago Torres-Arias December 22, 2021 Leave a comment on What is Log4j? A cybersecurity expert explains the latest internet vulnerability, how bad it is and what’s at stake Log4Shell is the latest hacker exploit rocking the internet, and it’s arguably the worst yet. The vulnerability is in an obscure piece of software used on millions of computers.